SYNOPSIS

DESCRIPTION

The syslog() function shall send a message to an implementation-defined logging facility, which may log it in an
implementation-defined system log, write it to the system console, forward it to a list of users, or forward it to the logging
facility on another host over the network. The logged message shall include a message header and a message body. The message header
contains at least a timestamp and a tag string.

The message body is generated from the message and following arguments in the same manner as if these were arguments to
printf(), except that the additional conversion specification %m shall be
recognized; it shall convert no arguments, shall cause the output of the error message string associated with the value of
errno on entry to syslog(), and may be mixed with argument specifications of the "%n$" form.
If a complete conversion specification with the m conversion specifier character is not just %m, the behavior is
undefined. A trailing <newline> may be added if needed.

Values of the priority argument are formed by OR'ing together a severity-level value and an optional facility value. If
no facility value is specified, the current default facility value is used.

Possible values of severity level include:

LOG_EMERG

A panic condition.

LOG_ALERT

A condition that should be corrected immediately, such as a corrupted system database.

LOG_CRIT

Critical conditions, such as hard device errors.

LOG_ERR

Errors.

LOG_WARNING

Warning messages.

LOG_NOTICE

Conditions that are not error conditions, but that may require special handling.

LOG_INFO

Informational messages.

LOG_DEBUG

Messages that contain information normally of use only when debugging a program.

The facility indicates the application or system component generating the message. Possible facility values include:

LOG_USER

Messages generated by arbitrary processes. This is the default facility identifier if none is specified.

LOG_LOCAL0

Reserved for local use.

LOG_LOCAL1

Reserved for local use.

LOG_LOCAL2

Reserved for local use.

LOG_LOCAL3

Reserved for local use.

LOG_LOCAL4

Reserved for local use.

LOG_LOCAL5

Reserved for local use.

LOG_LOCAL6

Reserved for local use.

LOG_LOCAL7

Reserved for local use.

The openlog() function shall set process attributes that affect subsequent calls to syslog(). The ident
argument is a string that is prepended to every message. The logopt argument indicates logging options. Values for
logopt are constructed by a bitwise-inclusive OR of zero or more of the following:

LOG_PID

Log the process ID with each message. This is useful for identifying specific processes.

LOG_CONS

Write messages to the system console if they cannot be sent to the logging facility. The syslog() function ensures that
the process does not acquire the console as a controlling terminal in the process of writing the message.

LOG_NDELAY

Open the connection to the logging facility immediately. Normally the open is delayed until the first message is logged. This
is useful for programs that need to manage the order in which file descriptors are allocated.

LOG_ODELAY

Delay open until syslog() is called.

LOG_NOWAIT

Do not wait for child processes that may have been created during the course of logging the message. This option should be used
by processes that enable notification of child termination using SIGCHLD, since syslog() may otherwise block waiting for a
child whose exit status has already been collected.

The facility argument encodes a default facility to be assigned to all messages that do not have an explicit facility
already encoded. The initial default facility is LOG_USER.

The openlog() and syslog() functions may allocate a file descriptor. It is not necessary to call openlog()
prior to calling syslog().

The closelog() function shall close any open file descriptors allocated by previous calls to openlog() or
syslog().

The setlogmask() function shall set the log priority mask for the current process to maskpri and return the
previous mask. If the maskpri argument is 0, the current log mask is not modified. Calls by the current process to
syslog() with a priority not set in maskpri shall be rejected. The default log mask allows all priorities to be
logged. A call to openlog() is not required prior to calling setlogmask().

Symbolic constants for use as values of the logopt, facility, priority, and maskpri arguments are
defined in the <syslog.h> header.